What caused the Stock Market Crash of 1929 that lead to the Great Depression?

The stock market crash of 1929 was due to a market that was overbought, overvalued, and excessively bullish, rising even as economic conditions were not supporting the advance. The crash began on October 24, when the market opened 11% lower. Institutions and financiers stepped in with bids above the market price to stem the panic, and the losses on that day were modest with stocks bouncing back the next two days. However, this bounce turned out to be illusory, as the following Monday, now known as Black Monday, the market finished down 13% with the losses exacerbated by margin calls. The next day (Black Tuesday), bids completely vanished, and the market fell another 12%. From there, the market trended lower until hitting bottom in 1932.

The stock market crash of 1929 and the ensuing Great Depression certainly altered an entire generation's perspective and relationship to the financial markets. In a sense, it was a total reversal of the attitude of the Roaring '20s, which had been a time of great optimism and economic growth.

In the first half of the decade, companies were doing excellent business exporting to Europe, which was rebuilding from the war. Unemployment was low, and automobiles were spreading across the country, creating jobs and efficiencies for the economy. Until the peak in 1929, stock prices went up by nearly ten times.

The economic growth created an environment in which speculating in stocks became almost a hobby, with the general population wanting a piece of the market. Many were buying stocks on margin--the practice of buying an asset where the buyer pays only a percentage of the asset's value and borrows the rest from the bank or a broker--in ratios as high as three to one, meaning they were putting down $1 of capital for every $3 of stock they purchased. This also meant that a loss of one-third of the value in the stock would wipe them out.

People were not buying stocks due to fundamentals; they were buying in anticipation of rising share prices. Rising share prices simply brought more people into the markets, convinced that it was easy money. In mid-1929, the economy stumbled due to excess production in many industries, creating an oversupply. Essentially, companies were able to acquire money cheaply due to high share prices and invest in their own production with the requisite optimism.

This overproduction eventually led to oversupply in many areas of the market such as farm crops, steel, and iron. Companies were forced to dump their products at a loss, and share prices began to falter. Due to the number of shares bought on margin by the general public and the lack of cash on the sidelines, entire portfolios were liquidated and the stock market spiraled downwards.